Exothermic reactions carried out in refining and/or petrochemistry require cooling by an additional fluid to prevent thermal runaway of the reactor in which they are conducted. It is also necessary to keep a homogeneous temperature gradient within the reactor in order to prevent the existence of hot spots in the catalyst bed. These hot spots can prematurely decrease the catalyst activity. They also lead to non-selective reactions. It is therefore important to hove at least one mixing chamber in a reactor that allows homogeneous temperature distribution of the fluids and cooling of the reaction fluids to a desired temperature.
In order to achieve this homogenization, the person skilled in the art is often led to use a specific layout of often complex internals comprising delivery of the quench fluid as homogeneous as possible in the reactor section. This injection is performed downstream from the mixing chamber, either through multi-hole systems such as those described for example in patent documents EP-B-0,716,881, U.S. Pat. No. 5,025,831, or through spider type systems such as those described for example in U.S. Pat. No. 4,836,989. These boxes are generally very complex. They are often double, or even triple, such as those described in U.S. Pat. No. 5,232,283, often provided with internals such as blades, fins, baffles or deflectors, as described for example in U.S. Pat. No. 5,567,396. The main drawbacks of this type of system are the complexity of development and implementation, the induced pressure drop and more particularly the overall dimensions (room taken up in the reactor).
A quench device allowing to provide efficient exchange between the quench fluids) and the fluid(s) of the process is also known from patent application FR-A-2,824,495. This device is integrated in an enclosure and it comprises a quench fluid injection rod, a fluid gathering baffle, the quench box proper, achieving mixing between the quench fluid and the downflow, and a distribution system consisting of a perforated tray and a distribution plate. The quench box comprises a deflector providing swirling of the fluids in a direction substantially non radial and non parallel to the axis of said enclosure and, downstream from the deflector, in the direction of circulation of the reaction fluid, at least one outlet passage section for the mixture of fluids formed in the box. This device allows to overcome some drawbacks of the various systems of the prior art, but it remains very bulky.
Some current devices allow overall dimensions to be reduced. For example, U.S. Pat. No. 6,881,387, EP-B-1,721,660 and U.S. Pat. No. 6,180,068 describe flatter mixing boxes than in the prior art. However, these quench boxes still include many internals likely to produce high pressure drops in order to be efficient.
The object of the present invention thus is to overcome one or more of the drawbacks of the prior art by providing a compact mixing device. The device according to the invention allows a substantial gain in terms of reactor dimensions and provides good mixing of the fluids, as well as good temperature homogeneity.